Unconscious forces are driving women into the arms of their lovers. Hidden factors influence sexual attraction, but we don’t often think about them. Women never suspect things such as genetic influences and monthly fertility cycles can be just as important to us as a winning smile or a toned six-pack. He has a great sense of humor and an infectious laugh, but are his immune system genes appealing to you? Read on for some of the surprising influences that make your man seem sexy to you.

Fertility Is a Big Influence

Let’s think about the time of the month. Feeling a powerful attraction to very masculine-looking men? You’re probably very fertile and likely to conceive. At the highest fertile point in your menstrual cycle, hormones are prompting you to seek out a mate with high-quality genes. That masculine face is an indicator of good genes, according to one study. When you are not fertile, you’re likely to go looking for a man whose facial features are more feminine.

Another study found fertility may also prod your interest in dating men of a different ethnic background. And another indicates fertile women also unconsciously prefer scents of men who have symmetrical body and facial features. Science is unclear on what are the chemical signals of symmetry, but science tells us symmetry is a sigh of health and genetic fitness.

Heredity Whispers in Your Ear

Let’s start with your Mom and Dad. They gave you a little thing called major histocompatability complex (MHC) genes. These genes are floating around in your immune system, and they play an important part in your sexual attraction to a partner. One recent study found evidence they influence you to seek out sexual partners who do not share your immune genes. Bringing in different immune genes to the gene pool apparently is a good thing from an evolutionary standpoint, and your genes are nudging you in that direction.

Mirror, Mirror on the Wall

Does your boyfriend resemble your Dad, your brother or even you? Studies indicate that genes drive women to search for men who look like their family members. The unconscious attraction can be traced to a woman’s search for genes that are somewhat similar to hers but still different enough to give reproduction the best chance for success.

If the idea sounds beyond icky, researchers say there’s no cause for alarm. The studies don’t indicate that women are attracted to their relatives. On the contrary, there is evidence that women even avoid their fathers when they are fertile, according to scientists. It’s the general physiognomy, not the relative per se, that women find appealing.

Read More: The Hidden Forces Driving Women’s Sexual Attraction